If this is the case than you should know better.Not if you are a photographer and get part of you income from photography
Know better than what, have you own web site, selling on line and in galleries? We are not talking about stupid people that post photos on Flickr but professional photographers whom do no better. I sell on my web site, if any photos are used as wallpaper without my consistent, it is stealing
Not at all, if you post a photo online then people can do whatever they want with it. I have a ton of pictures on my laptop, and I only took a couple of them. Did I steal them? No.
No you can not do anything you want with them and Yes you did steal. Read the photography copyright laws. If is it not a free stock photo and states that on the site and you did not ask permission it is steeling.
I require consent for use of any of my photos in anyway. Some people like friends have asked to use mine as wallpaper and I tell them yes. The thing is you have to ask permission. When I do work for any architectural companies I write a stipulation that they can reproduce my photos for marketing purposes or for using in the building for hanging works but all photos have to be accredited to me if reproduced with my name and company as being the photographer.
If you think it is OK using someone else’s photos for what ever you want think about this. Spend $500 on a tripod, $500 on a lens, $1000 on a DSLR, another $2000 on packs, cable releases, filters, memory cards, software. Then drive 2 hours to climb down a mountain to take photos of a waterfall that took all day long. Then work on the photos for hours at home on a computer. Then have someone take them and do whatever they want with them. Don’t think so.